This invention relates to a method for the suspension polymerization of vinyl chloride or a monomer mixture having vinyl chloride as the main component with one or more copolymerizable monomers, in which polymer scale is prevented from depositing on the walls and other surfaces in contact with the monomer or monomers in a polymerization reactor.
In the preparation of polyvinyl chloride resins, various methods including suspension polymerization, emulsion polymerization, solution polymerization, gas-phase polymerization and bulk polymerization are known. However, none of these prior art methods has been free from the problem of polymer scale deposition. According to the prior art methods, the surfaces in contact with monomer, including the inner walls of the reactor, and surfaces of the agitator in the reactor usually become covered with polymer scale during the polymerization runs, resulting in decreasing polymer yields and the lowering of the cooling capacity of the reactor. Further, pieces of the polymer scale so deposited eventually come off the surfaces and enter into the resulting polymer product thereby degrading its quality. Furthermore, the cleaning of the polymerization reactor to remove the polymer scale after each polymerization run not only requires extensive labor and time but also involves a serious health problem for workers due to the toxicity of the unreacted monomer absorbed in the polymer scale.
According to another prior art method, prevention of polymer scale deposition on the inner walls and other surfaces of a polymerization reactor has been attained by coating the surfaces prior to each polymerization run with a compound selected from polar organic compounds such as amines, quinones and aldehydes; and organic dyes and pigments (see U.S. Pat. No. 3,669,946). This method is disadvantageous because of the (1) troublesome drying procedure which must be followed after each coating and (2) lowered productivity of the polymerization reactor as a result of the relatively long period of time spent in the coating process between polymerization runs. In addition, environmental pollution and health problems are caused by the large amounts of organic solvents employed with the coating compounds.